I haven't been successful in stretching toe boxes more than about 1/2 size (i.e., 1/6 inch). Then again, I don't have the heavy duty bench tools a high end pro shop or downhill ski shop has - just a ball and ring pliers (also called hoke and ball pliers, or bunion stretcher) and a cautiously applied hair drier to warm the desired spot. But one experienced pro also quoted 1/2 size stretchability in the toe box to me.
(My info is not specific to SP Teris, which I've never owned.)
If you tell SP Teri what model boot you have, they can tell you whether they are nominally heat mold-able, and at what temperatures. If you can't find a model name on them, you might find a serial number, or maybe they can tell from a picture.
If they say no, it gets trickier.
BTW, where are they snug? Is it at the front of the toe, the sides, or both? That's very important. If you just need to stretch a little bubble sideways next to the front of the big or little toe, that's quite routine at many pro shops.
A good pro shop can often do a good job of heat molding and/or stretching your boots, if there is one within a few hours drive of you. There is obviously a greater risk for inexperienced crafts people like (I assume) yourself.